JPS62226827A - Method and device for producing optical element - Google Patents

Abstract

PURPOSE:To obtain the titled optical element in a short time by cooling an optical element while keeping the non-optical face of the element at a temp. higher than that of the optical face during cooling to prevent the generation of internal stress when the optical element made of glass is produced by molding. CONSTITUTION:A glass material for molding the optical element is supplied into the cavity formed between plural molding members such as barrel dies 2 and 6 and forming dies 4 and 5, and heated and softened to produce the optical element 1 by molding. When the element is cooled, the non-optical face 8 of the glass optical element 1 which is not used for the transmission or reflection of light is heated by a heater 3 provided in the barrel die 2, and kept at a temp. higher than that of the optical face 7 which is used for the transmission or reflection of light. Under such conditions, the element is cooled. Consequently, the stress generated in the optical element 1 is relieved while only the non-optical face 8 is deformed, and the optical element 1 having the optical face 7 with excellent form precision can be obtained.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method and apparatus for manufacturing an optical element, and in particular, to a method and apparatus for manufacturing an optical element. The present invention relates to a method and apparatus for manufacturing an optical element by supplying the glass element, heating and softening the glass element, and molding the glass element.

(Prior Art) Conventionally, in this type of manufacturing method and apparatus, an optical element has been manufactured through a process of molding a heated and softened glass material and then uniformly cooling the entire molded material. This method and device have already achieved many results in small-diameter lenses for cameras, reading relenses for compact discs, and the like.

(Problems to be solved by the invention) However, in the conventional manufacturing method and apparatus as described above,
It has been considered difficult to mold relatively large optical elements. The reason for this is that as the optical element becomes larger, the temperature difference between the center and the vicinity of the surface increases during cooling, which generates stress inside. If there is internal stress, optical birefringence will occur, which is a major drawback as an optical element. or,
Although some of the stress may be released during cooling, there is a drawback that in this case the surface shape accuracy required as an optical surface is lost.

The above two drawbacks can be overcome by slowing down the cooling rate, since the temperature difference between the center and the surface of the optical element does not become too large. However, slowing the cooling rate increases the time required to mold one optical element, which is a major drawback for mass production.

(Objective of the Invention) The present invention eliminates the drawbacks of the conventional optical element molds described above, and without slowing down the production speed of optical elements.
Another object of the present invention is to provide a method and apparatus for manufacturing an optical element without generating internal stress.

(Means for Solving the Problems) As a means for solving the above-mentioned problems, the method for manufacturing an optical element according to the present invention is such that when cooling a large glass optical element after molding, the light of the optical element is transmitted through the optical element. Alternatively, a method is adopted in which a surface that does not reflect light (hereinafter referred to as a non-optical surface) is kept at a higher temperature than a surface that transmits or reflects light (hereinafter referred to as an optical surface) while being cooled. When cooling is performed in this manner, the stress generated inside the optical element is released by deforming only the non-optical surface, and as a result, the internal stress is negligibly small and the optical element has sufficiently good shape accuracy. A glass optical element with a surface is obtained. By employing such a cooling method, a large-sized optical element can be manufactured in about the same amount of time as the aforementioned small-sized optical element.

(Summary of the Invention) A method for manufacturing an optical element according to the present invention includes supplying a glass material for molding an optical element into a cavity formed between a plurality of mold members, heating and softening the glass material, and molding the optical element. In the method of manufacturing, when a glass material is heated and softened and formed by molding and then cooled, a non-optical surface that is not used for transmitting or reflecting light of the glass optical element is Alternatively, the optical surface is cooled while being maintained at a higher temperature than the optical surface used for reflection.

Further, the optical element manufacturing apparatus according to the present invention supplies a glass material for molding an optical element into a cavity formed between a plurality of mold members, heats and softens the glass material, and manufactures an optical element by molding. In the apparatus, a heating means is disposed in a mold member in contact with a non-optical surface of an optical element, and the heating means is energized during cooling after heating and softening the optical element and forming an optical element by molding. It is characterized in that the non-optical surface of the optical element is cooled while being kept at a higher temperature than the optical surface.

(Example) Hereinafter, details of the present invention will be explained with reference to examples.

The following explanation relates to an example in which the present invention is applied to molding a biconcave lens, but the present invention can be applied not only to lenses of other shapes but also to pentaprisms for cameras or laser beams, as will be explained later. It can also be applied to toric lenses of printers, etc.

FIG. 1 is a cross-sectional view showing the lateral movement of the mold in an embodiment of the present invention, in which 1 is a molded biconcave lens, 2 is a mold that holds the lens 1, and 3 is a mold that is wound around the mold 2. 4 and 5 are molds, and 6 is a mold for holding the mold 4.

Note that ceramic coatings are applied to the upper and lower surfaces of the mold 2 to provide thermal insulation between the mold 5 and the mold 6, respectively.

FIG. 2 shows a biconcave lens obtained using the mold structure shown in FIG. 1, in which 7 is an optical surface and 8 is a non-optical surface.

The glass material used in this example is a heavy flint type glass material, and the predetermined dimensions of the zero biconcave lens are a diameter of 40 mm, a center wall thickness of 4.3 mm, and a peripheral wall thickness of 8.6 mm.

The procedure of this example is as follows.

After the lens 1 is molded (500° C.), cooling begins at a predetermined rate. At this time, the heater 3 is energized so that the portion of the lens 1 of adjustment type 2 in contact with the non-optical surface is maintained at 500°C. When the temperature near the optical surface of the lens 1 reaches 500-61° C., cooling is performed while energizing the heater 3 so that the temperature difference between the non-optical surface and the optical surface of the lens 1 is maintained at ΔT. Cooling with such a temperature difference ΔT does not need to be carried out to room temperature, and may be canceled once the temperature reaches a temperature at which deformation due to viscosity does not occur. In this example, as a guideline for the temperature, the heater 3 was turned off and ΔT was set to 0 at a temperature (410° C.) that was 10° C. or more lower than the glass inversion point.

The results of this example are shown for ΔT of 10° C., 5° C., and 0° C. (that is, in the case of conventional uniform cooling with zero temperature difference).

Here, all the maximum surface shape changes are inward.

From this result, it is clear that increasing ΔT has the effect of keeping the precision of the optical surface 7 favorable. Especially △T is 1
At 0° C., the internal stress expressed in terms of birefringence is approximately 4 nm, which is sufficient for use as a camera lens. The non-optical surface 8 is presumed to be deformed, although it cannot be seen with the naked eye.

Incidentally, when ΔT was 10° C. and 5° C., the surface shape of the peripheral portion was slightly distorted, but this seems to be due to the effect of heating the non-optical surface. This seems to be a drawback of this method that requires attention.

The essential point of the present invention is to make the temperature of the non-optical surface higher than the temperature of the optical surface during cooling. Therefore, the means thereof are not necessarily limited to the above embodiments.

For example, if one end of a material with good thermal conductivity, such as copper, is brought into contact with a low heat source and the other end is brought into contact with molds 4 and 5 in FIG. The temperature of the optical surface can be lower than that of the non-optical surface because heat flows to the low heat source.

Alternatively, the mold 2 of the above embodiment may be made of a heat-generating material. For example, if the mold 2 is made of molybdenum and a current is passed through it, the mold 2 itself will be heated and the same effect as in the previous embodiment can be obtained.

On the other hand, the shape of the optical element is not limited to the lens shape. A camera pentaprism consists of six optical surfaces and one non-optical surface. The toric lens of a laser beam printer consists of two optical surfaces and four non-optical surfaces.

In any case, the object of the present invention can be achieved by taking measures to make the temperature of the non-optical surface higher than the temperature of the optical surface according to the shape of the optical element.

(Effects of the Invention) As explained above, the present invention uses a simple method of cooling the non-optical surface while keeping the non-optical surface at a higher temperature than the optical surface when manufacturing an optical element by molding. By achieving the effect of preventing the collapse of surface shape accuracy, large-sized optical elements made of glass can be manufactured in a short time.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of the mold structure of a mold for producing a large glass optical element according to the present invention, and FIG.
This is a glass optical element molded using the mold shown in the figure. 1... Glass optical element 2... Adjustment mold 3... Heater 4... Molding mold 5... Molding mold
6... Trunk wall 7... Optical surface
8...Non-optical surface agent Teruo Taniyama Pagishi 1) Correct line: i°゛-'Ro Figure 1 Figure 2

Claims (2)

[Claims] (1) In a method of supplying a glass material for molding an optical element into a cavity formed between a plurality of mold members, heating and softening the glass material, and manufacturing an optical element by molding, the glass material is heated and softened. When cooling after forming by molding, the non-optical surfaces of the glass optical element that are not used for transmitting or reflecting light are heated to a higher temperature than the optical surfaces of the glass optical element that are used for transmitting or reflecting light. A method for manufacturing an optical element characterized by cooling while maintaining the same. (2) In an apparatus for manufacturing an optical element by supplying a glass material for molding an optical element into a cavity formed between a plurality of mold members, heating and softening the glass material, and molding the non-optical surface of the optical element. A heating means is disposed in the mold member in contact with the optical element, and after the optical element is heated and softened and the optical element is formed by molding, the heating means is energized to make the optical element more non-optical than the optical surface of the optical element. An optical element manufacturing device characterized by cooling the surface while keeping the surface at a high temperature.